If I enable access to plugins to a child network. The super admin is having the access to Plugin " Editor " and also ability to delete the plugins. What if he accidentally delete's or edit the plugin which affects the entire Multi-site installation?

1) Is there an option which the changes made for just that Child network only and the entire Multisite? I mean that every plugin system works separately

You update the options for each Network by going to a site in the network and then going to the Network Admin | Settings menu.

As to your followup, the plugins for each network use shared code. If the super admin from one network modifies a plugin, it will be changed for all other sites using it, regardless of network. This goes for themes as well. You should assign super admin privileges with care.

There is probably a way to disable plugin and theme editing, but it is outside the scope of this plugin.